Metals and Materials International

A scale-bridging technique was used to investigate the effect of the elastic properties of β-Ti alloys on the stress distribution around the femoral stem of an artificial hip joint with a simplified geometry when under an external loading. The anisotropic elastic constants of single-crystalline β-Ti alloys (TN1: Ti-18.75 at% Nb, TN2: Ti-37.5 at% Nb, and TN3: Ti-43.75 at% Nb) were calculated using an ab-initio technique that was based on density functional theory calculation. The single-crystalline elastic constants calculated via the ab-initio technique were used to calculate the elastic constants of polycrystal β-Ti alloys using an elastic selfconsistent scheme. Finite element analysis based on the elastic constants of polycrystalline β-Ti alloys for a femoral stem was conducted to calculate the above-mentioned stress distribution. The model system consisting of a TN1 alloy exhibited a relatively high level of von Mises stress on the surface of cancellous and cortical bones compared to model systems consisting of TN2, TN3 alloys and commercial biomaterials (Ti-6Al-4V alloy and 316STS). The thickness of the cancellous bone between the femoral stem and the cortical bone affected the stress concentration on the surface of the cortical bone.

Finite strain deformation behaviour of recycled aluminium alloy AA6061 is investigated in this paper via uniaxial tensile test and Taylor cylinder impact test implementations. The uniaxial tensile tests are performed at different elevated temperature from 100 to 300 °C, at the strain rate of 10−4 s−1 and 10−3 s−1 and the Taylor cylinder impact tests are conducted at different impact velocity ranging from 170 to 370 m/s. The deformation behaviour of tensile test specimen is evaluated in term of the stress–strain curve and the anisotropic behaviour, including fracture mode, of the impact test specimen, is analyzed according to the geometric profile of the deformed specimen. Besides, the damage characteristic of both the experimental tests is characterized using Scanning Electron Microscope analysis and ImageJ software analysis. The recycled AA6061 exhibits strain-rate dependency behaviour and strong anisotropic behaviour. The flow stress and damage evolution are enhanced with the increment in strain rate. The anisotropic behaviour of such recycled material can be observed in the deformed specimen of impact test, where a non-symmetrical (ellipse shape) footprint is observed. Moreover, the damage is initiated in the undeformed specimen and it getting severe when a deformation is applied. This is due to the growth and coalescence of the micro-voids in the material resulting in formation of micro-cracks and dimples and increase in number of micro-voids.

The expansion of a metal tube by means of an electromagnetic forming (EMF) process is attractive because EMF has a high forming rate and can reduce residual stress. The forming forces in EMF are Lorentz forces. They are derived from a repulsive interaction between a transient electric current induced in a coil with the aid of a capacitor bank and an eddy current induced in a metal tube by means of a transient current. Highly conductive metals are suitable for EMF-based tube expansion but tubes of low conductive metals are often used for industrial purposes. We studied various methods of using EMF to increase the formability of low conductive metals. In particular, we used a finite element method to compute an electromagnetic field coupled with temperature and deformation of a metal tube. Our results show that a highly conductive layer can increase the formability of a low conductive metal.

The microstructure and texture of different rolling processes in situ Cu–15Cr sheets are studied. The results show that the second phase Cr in the material gradually become broken, flattened, merged and homogenized from dendritic state to oriented thin lath. Meanwhile, the texture in distributed copper matrix grains finally forms Brass {110}<112>, Goss {001}<110> and Copper {112}<111> textures along with Cr phase texture of randomly distributed α-fiber (<110> fiber) and γ-fiber (<111> fiber) texture. Based on VPSC (visco-plastic self-consistent model), the texture of cold rolled Cu–15Cr composite is simulated, and the simulation result indicates that obvious twinning effect in the copper matrix appears with a feature of a special texture evolution law of Goss.

Các tiếp xúc ohmic Pd/Ge/Pd/Ti/Au và Pd/Si/Pd/Ti/Au cho InGaAs loại n đã được nghiên cứu cho các ứng dụng trong tiếp xúc ohmic của bộ phát HBT AlGaAs/GaAs. Trong tiếp xúc ohmic Pd/Ge/Pd/Ti/Au, một điện trở tiếp xúc đặc trưng tối thiểu là 1.1×10−6 Ωcm2 đã đạt được bằng cách thiêu kết ở 425°C trong 10 giây, nhưng hiệu suất ohmic hơi giảm khi nhiệt độ thiêu kết tăng do phản ứng giữa các vật liệu tiếp xúc ohmic và nền InGaAs. Tuy nhiên, một giao diện phẳng không mọc nhọn và tiếp xúc ohmic tương đối tốt (cao-10−6 Ωcm2) đã được duy trì sau khi thiêu kết ở 450°C trong 10 giây. Trong tiếp xúc ohmic Pd/Si/Pd/Ti/Au, mặc dù chiều cao vật cản của mối nối kim loại-InGaAs thấp hơn, các tiếp xúc đã được lắp đặt cho thấy hành vi không phải ohmic do sự hiện diện của lớp Si cách điện. Tuy nhiên, điện trở tiếp xúc đặc trưng đã giảm đáng kể xuống 4.3×10−7 Ωcm2 bằng cách thiêu kết ở 425°C trong 10 giây. Điện trở tiếp xúc đặc trưng tối thiểu 3.9×10−7 Ωcm2 đã đạt được bằng cách thiêu kết ở 400°C trong 20 giây. Hiệu suất RF của HBT AlGaAs/GaAs cũng đã được kiểm tra bằng cách sử dụng các hệ thống Pd/Ge/Pd/Ti/Au và Pd/Si/Pd/Ti/Au làm tiếp xúc ohmic cho bộ phát. Tần số cắt lần lượt là 65.0 GHz và 74.4 GHz, và tần số dao động tối đa lần lượt là 51.3 GHz và 52.5 GHz, cho thấy hoạt động tần số cao rất thành công.

Extruded AZ31 Mg alloy rods were subject to free-end torsion deformation at room temperature. The microstructure features of the torsion deformed samples were characterized using electron backscatter diffraction technique. Mg rods with gradient microstructure can be fabricated by torsion deformation. Inhomogeneous distribution of microstructure along the radial direction of the twisted rods is attributed to the linearly increasing strain accumulation and strain rate from core to surface. With increasing equivalent strain, both the amount of {10-12} twins and dislocation density increase and the c-axes of texture tend to rotate towards torsion axis. Although both dislocation slips and {10-12} twinning can be activated during torsion, dislocation slips are considered as the dominated deformation mechanism and responsible for the change of macro-texture for present torsion deformation. {10-12} twins and dislocations in the twisted samples can generate refinement hardening and dislocation hardening, respectively, to increase the hardness value.

In this work, specimens of the 2024 aluminum alloy sheet were compressed and stretched along the original rolling direction at elevated temperatures. The microstructure evolution was investigated by characterizing the metallographic structures via electron backscattered diffraction technology before and after deformation. It was found that while recrystallization occurred in the compressed specimens, it was not observed to the same extent in the stretched specimens. This difference in the grain morphology has been attributed to the different movement behaviors of the grain boundaries, i.e., their significant migration in the compression deformation and the transformation from low-angle to high-angle boundaries observed mainly during tension deformation. The empirical model, which can describe the grain size evolution during compression, is not suitable in the case of tension, and therefore, a new model which ignores the detailed recrystallization process has been proposed. This model provides a description of the grain size change during hot deformation and can be used to predict the grain size in the plastic deformation process.